Large Range Of Frequencies With Two Counters - National Instruments DAQ X Series User Manual

Figure 7-13 illustrates this method. Another option is to measure the width
of a known period instead of a known pulse.
Pulse Gate
fx Source
Pulse-Width
Measurement

Large Range of Frequencies with Two Counters

By using two counters, you can accurately measure a signal that might be
high or low frequency. This technique is called reciprocal frequency
measurement. When measuring a large range of frequencies with
two counters, you generate a long pulse using the signal to measure. You
then measure the long pulse with a known timebase. The X Series device
can measure this long pulse more accurately than the faster input signal.
Counter 0 is always paired with Counter 1. Counter 2 is always paired with
Note
Counter 3.
You can route the signal to measure to the Source input of Counter 0, as
shown in Figure 7-14. Assume this signal to measure has frequency fx.
NI-DAQmx automatically configures Counter 0 to generate a single pulse
that is the width of N periods of the source input signal.
© National Instruments
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
Width of Pulse (T )
Pulse
1 2 ...
fx
Width of
T =
Pulse
Frequency of fx =
Figure 7-13. High Frequency with Two Counters
7-15
Chapter 7 Counters
N
N
fx
N
T
X Series User Manual